The present invention relates to a hard disk drive, particularly a hard disk drive for use as a storage unit in an information processor or the like. More particularly, the present invention is concerned with a hard disk drive having an enhanced reliability against environmental changes.
A hard disk drive mainly comprises a magnetic disk serving as a storage medium and a magnetic head for read and write. It further comprises a rotating mechanism for the magnetic disk and a positioning mechanism for the magnetic head. These components are disposed within an enclosure. A hard disk drive is connected to a personal computer or another information device and is used as a main memory, for which a high reliability is required.
Particularly, in the case where a hard disk drive is mounted on a mobile personal computer, it is exposed to various external environments. Therefore, it is important that the reliability of the hard disk drive should not be deteriorated against environmental changes. Typical examples of such environmental changes include a change in temperature, a change in atmospheric pressure, a change in humidity, and whether a trace of contamination component is present or not.
As to the contamination component, typical examples are corrosive gases which are deposited as contamination on the surfaces of the magnetic head and the magnetic disk, causing corrosion and trouble of the head and the disk, such as various organic gases and organometallic gases, as well as particles which get into the gap between the magnetic disk and the magnetic head, causing damage. For preventing a bad influence of these components, the enclosure of the hard disk drive has a semi-sealed structure usually through a very small vent hole called a breather hole. In the interior part (inside) of the enclosure are disposed an adsorbent for adsorbing harmful gas components and a filter unit for removing particles, whereby the harmful contamination component is removed to keep the inside of the hard disk drive clean and prevent the deterioration of reliability caused by the contamination component.
In JP-A No. H7-287976 there is disclosed a hard disk drive wherein a filter unit having an expansion chamber serving as a buffer is disposed outside a breather hole, allowing corrosive gases invaded from the exterior to stay in the expansion chamber, thereby further suppressing the entry of contamination component from the exterior part (outside) to the inside of the enclosure.
Since the concentration of the contamination component is usually very low, it can be fully suppressed by the above structure. With the above enclosure, however, it is difficult to ensure a high reliability against a change in external humidity. In the interior of the enclosure is provided a water adsorbent for adsorbing water, whereby the inside of the enclosure is normally held at a low humidity. But a high humidity environment must be taken into consideration as an external environment of the hard disk drive and in this case a gradual entry of external high-concentration water into the enclosure is unavoidable. Particularly, when the hard disk drive is left standing for a long period under a high humidity environment, it is impossible to remove water completely with a limited amount of the water adsorbent. Upon saturation of the water adsorbent the humidity in the interior part of the enclosure becomes almost equal to the environmental humidity. If the hard disk drive is further left standing in this state, corrosion of the magnetic head and the magnetic disk is accelerated. This is a great cause of loss in reliability of the hard disk drive.
In JP-A No. H5-12848 there is disclosed a hard disk drive wherein a heater is provided within a water adsorbent unit communicating with both inside and outside of an enclosure, and at the time of regenerating the water adsorbent periodically by the heater, breather holes for breathing from the water adsorbent unit to the inside and outside of the enclosure are controlled for opening and closing with use of a shape memory alloy which is deformed with heat of the heater. In this conventional hard disk drive, when the breather hole from the water adsorbent unit to the outside of the enclosure is closed, there is provided a hermetically sealed structure wherein the interior of the enclosure and the water adsorbent unit are connected together. When heating is performed with the heater at the time of regenerating the water adsorbent, the breather hole to the outside of the enclosure is opened, while the breather hole to the inside of the enclosure is closed, so that only the enclosure is hermetically sealed and water released from the water adsorbent is discharged to the outside of the enclosure, whereby, according to this prior art publication, the inside of the enclosure is always maintained at a low humidity, the accumulation of water in the interior part of the enclosure is prevented, and corrosion resistance is improved. In this conventional hard disk drive, however, since the enclosure is always sealed hermetically, there is a technical problem such that the occurrence of a pressure difference between the inside and the outside of the enclosure is unavoidable due to a change in external temperature or in external atmospheric pressure.
From the standpoint of preventing the entry of harmful components into the enclosure it is desirable that the hard disk drive have a completely sealed structure. However, in the case of a completely sealed structure, a pressure difference between the inside and the outside of the enclosure occurs due to a change in external temperature or in external atmospheric pressure, with consequent likelihood of a change in floating quantity of the magnetic head due to deformations of the enclosure and peripheral mechanical parts or the occurrence of data error due to a worsening in positioning accuracy of the magnetic head.
In JP-A No. H5-314751 there is disclosed a hard disk drive wherein, as an enclosure sealing structure, a pressure regulating mechanism is provided, such as connecting the inside and the outside of an enclosure through a movable cylinder or disposing an elastic structure in part of the sealing structure, to prevent the occurrence of a pressure difference between the inside and the outside of the enclosure caused by a change in external temperature or pressure. However, the hard disk drive is usually required to tolerate an external temperature change from about −5° C. to about +60° C. and an external atmospheric pressure change of about 3,000 m altitude (about 0.7 atm.). For maintaining both internal and external pressures of the enclosure constant even under these conditions, it is necessary for the pressure regulating mechanism to be able to absorb a volumetric change of ±30% or more, so that the mechanism itself becomes very large in size. Therefore, the application thereof to a small-sized hard disk drive is difficult.